In the prior art, winding coils in the electrical machine are cooled with cooling oil. In most of the oil passage designs for cooling winding coils in the electrical machine, there are often a number of 90-degree corners in the oil passage from the oil inlet hole to the oil outlet hole, causing the cooling oil to lose pressure. Thus, the cooling oil will not be sprayed onto the winding coils from the oil outlet hole but naturally flow out by gravity.
FIG. 1 is a schematic diagram of the housing and stator assembly of the electrical machine in the prior art. As shown in FIG. 1, a number of winding coils 6 are arranged along the internal arc line of the housing 11 of the electrical machine. FIG. 1 does not show a casing end cover.
FIG. 2 is a sectional view taken along a line AA′ shown in FIG. 1. As shown in FIG. 2, the housing 11 of the electrical machine comprises: a casing 1, an oil inlet hole 7, oil passages 2 (guiding passage of the cooling oil), oil outlet holes 3, a stator retainer 8 and a casing end cover 10. The electrical machine shown in FIG. 2 further comprises a stator assembly connected to the housing and formed by a stator iron core 5, winding coils 6 and slot insulations. In the sectional view of FIG. 2, the slot insulations cannot be seen as they are not drawn therein. In addition, FIG. 2 show the path taken by the cooling oil from the oil inlet hole 7 through the oil passage 2 to the oil outlet holes 3 indicated by arrows.
FIG. 3 is a sectional view taken along a line BB′ shown in FIG. 2. FIG. 3 shows a casing 1, an oil passage 2, oil outlet holes 3, winding coils 6, a stator retainer 8 and slot insulations 12, indicated by arrows the path along which the cooling oil flows from the oil inlet hole 7 through the oil passage 2 to the oil outlet holes 3 and meanwhile indicates the path along which the cooling oil loses along the circumferential wall of the housing due to surface tension effects. This is because at an oil outlet hole located in a certain angle of the circumference, the oil when flowing out of the oil outlet hole may flow along the circumferential wall of the housing and the casing end cover due to the surface tension of the oil instead of pouring/spraying directly onto the winding coils.
At present, in some designs, grooves are provided below the winding coils. These grooves may accumulate some oil for the purpose of cooling the winding coils by immersing them into the oil. However, it is not easy to mount and manufacture these grooves, especially to ensure that the coils should not be touched when mounting the grooves so as to prevent from destroying the insulation of the coils. Furthermore, as the bottom of the coils is usually very close to the air gap of the electrical machine, the grooves should not affect the space of the air gap, either. In addition, after having cooled the top winding coil, the cooling oil that is heated by taking heat from said winding coil will flow along the circumferential grooves into the next winding coil to cool it, and so on. This leads to uneven cooling on every winding coil.
In conclusion, the cooling efficiency is not high in the existing solutions for cooling the winding coils of the electrical machine, leading to poor thermal durability of the electrical machine.